A pressure regulator, which is also referred to as “regulator”, is used for regulating a pressure of compressed air which is supplied from an air pressure source to be a specified pressure, and for supplying the regulated air to a pneumatic equipment such as pneumatic cylinder. This pressure regulator has, for example, as disclosed in Patent Document 1 and Non-patent document 1, a main valve body opening and closing a communication hole through which a primary port to which compressed air is supplied and a secondary port to which a pneumatic equipment is connected communicate with each other, and a spring force for closing the communication hole is supplied by a main valve spring member to the main valve body. The pressure regulator has a diaphragm for partitioning and forming a secondary pressure chamber to which a pressure of the secondary port is supplied, and a main valve shaft provided with the main valve body abuts on the diaphragm.
A pressure regulator in which the diaphragm is directly driven by a pressure regulating spring member in an axial direction of the main valve body acts as “direct acting type pressure regulator”. In this direct acting type pressure regulator, an inner space is partitioned into a secondary pressure chamber and an atmospheric pressure chamber by the diaphragm, and the diaphragm is formed with a relief hole. The relief hole is closed by causing a tip end of the main valve shaft to abut on the diaphragm, and a spring force is applied to the diaphragm in a direction to open the main valve body via the main valve shaft by the pressure regulating spring member. When the pressure of the secondary port drops below a set value, the diaphragm is displaced by the spring force of the pressure regulating spring member. At this moment, the main valve shaft is dislocated by the dislocation of the diaphragm, and the main valve body releases the communication hole. Then, compressed air of the primary port is discharged to the secondary port. When the pressure of the secondary port becomes equal to a set pressure, the diaphragm is displaced in a direction to detach from the main valve body by the pressure of compressed air which is applied to the diaphragm. As a result, the main valve body closes the communication hole.
In the above-described direct acting type pressure regulator, a total of the secondary pressure which is applied to the diaphragm, a primary pressure which is applied to the main valve body, and a spring force of the main valve spring member is applied as a thrust in a direction to close the main valve body. On the other hand, a total of the spring force of the pressure regulating spring member and the pressure of the secondary port, which is applied to the valve body, is applied as a thrust in a direction to open the main valve body.